OPTIMALLY DECOUPLED ROBUST-CONTROL OF MIMO PLANTS WITH MULTIPLE DELAYS

A two-stage procedural design method is proposed for optimally decoupl ed, robust multivariable control of a (stable or unstable, minimum pha se or nonminimum phase) plant with multiple delays. At the first stage , an optimal decoupler is designed for minimising the cross coupling e ffect. A modified characteristic loci method is next applied during th e second stage to complete the design. The present approach distinguis hes itself from the prevailing approaches such as LQG/LTR and H(infini ty) design by its unique merits that: (i) the cross coupling effect is minimised; (ii) this approach could be applied to those plants with m ultiple delays; (iii) a straightforward robustness criterion is integr ated into the design methodology which would consequently lead to a ro bustly stable design; and (iv) this approach gives a necessary conditi on for the resultant controller to be both stable and of minimum phase . In a wide class of problems this condition is also sufficient for a stable, minimum phase controller.